Concave soldering iron tip and method of soldering using same

ABSTRACT

In accordance with a preferred embodiment of the present invention, a concavity of an elliptical shape is formed in a chisel-shaped soldering tip to create a reservoir in which a quantity of molten solder is retained by surface tension. In a preferred method of use, the leads of an electronic component and the lands of a circuit board to which they are to be electrically connected are pretreated with flux. The tip, with a blob of solder in its concavity, is drawn along the lead/land region with the blob of molten solder making contact therewith, so that molten solder is wicked into the region, and joints are formed between the leads the lands.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of soldering electroniccomponents using hand-held soldering irons, and tips for such solderingirons of the type having a chisel-type shape.

2. Description of Related Art

A wide variety of soldering tips of differing sizes and shapes are knownfor use with soldering irons; see, for example, TIP CATALOG FORSENSATEMP SYSTEMS, PACE, Inc., Feb. 19, 1992. These tips, which areusually plated with iron, are usually tinned with solder for producing asoldered joint. However, these tips can hold only a limited amount ofsolder so that the solder will run out after only a few joints areformed, and solder will have to be reapplied to the tip. On the otherhand, if too much solder is applied to the tip, it will drip off whenthe tip is positioned to solder. Furthermore, there is no way to controlthe amount of solder that will flow from the tip, so that, when morethan a minimal quantity of solder is on the tip, there is a tendency fortoo much solder to be applied in a way that creates solder bridgesbetween adjacent joints, and a solder connection between two separatejoints forms a short.

Numerous instances of the use of hollow solder-containing tips are knownin the art, as can be seen by reference to U.S. Pat. Nos. 2,905,799 toDe Rugeris, 3,003,049 to Thomas, 3,580,462 to Vanyi, 4,648,545Polckemann, 4,699,308 to Wigley et al., and 4,936,501 to Babarinier.However, for the most part, these devices are not well suited to use insoldering electrical components since the tips cannot be appropriatelyshaped and they, also, would be prone to the creation of solder bridgesbetween adjacent connections. Still further, the solder-containing tipsof the soldering irons are not designed as interchangeable tips that canbe used with other, existing soldering irons as a replacement tip.

Thus, there is a need for a soldering tip which will have an increasedsolder-carrying capacity but which will not be prone to the formation ofsolder bridges between adjacent connections.

SUMMARY OF THE INVENTION

In view of the foregoing, it is a primary object of the presentinvention to provide a soldering tip with a recess that retains solderby surface tension.

It is a further object to provide a soldering tip having a concavityfrom which molten solder can be drawn by capillary(-like) action into aregion between a lead and a land to thereby form a solder joint.

In accordance with a preferred embodiment of the present invention,these and other objects are achieved by the provision of a concavity ofan elliptical shape in a chisel-shaped soldering tip. In a preferredmethod of use, the leads of an electronic component and the lands of acircuit board to which they are to be electrically connected,advantageously, may be pretreated with flux. The tip, with a quantity ofmolten solder in its concavity, is drawn along the lead/land region withthe quantity of molten solder making contact therewith so that moltensolder is wicked into the region and joints are formed between the leadsand the lands.

These and further objects, features and advantages of the presentinvention will become apparent from the following description when takenin connection with the accompanying drawings which, for purposes ofillustration only, show a single embodiment in accordance with thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a soldering tip in accordance with a preferredembodiment of the present invention;

FIG. 2 is a side elevational view of the soldering tip of FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 3--3 in FIG.2;

FIG. 4 is an elevational view in the direction of an oblique end face ofthe soldering tip of FIG. 2, i.e., parallel to line 3--3;

FIG. 5 is an enlarged cross-sectional view taken along line 5--5 in FIG.4;

FIG. 6 is a perspective view of a hand-held soldering device with asoldering tip in accordance with the present invention; and

FIGS. 7&8 are views illustrating steps in the performance of the methodof soldering in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-5 illustrate a soldering tip 1 for a hand-held soldering device,such as the soldering iron 5 shown in FIG. 6. Tip 1 is formed of a rodof thermally conductive material, such as copper, that has beenoverplated with iron and then nickel with the shank portion 1a beingthen overplated with chrome and the tapered working end dipped insolder, as is conventional for soldering tips. Furthermore, the workingend 1b is been machined to form an oblique surface 10, which forms, forexample, an angle θ with respect to a line which is normal to thelongitudinal axis of the tip 1, thereby giving the tip 1 a chisel shape.

In accordance with the invention, to increase the quantity of solderthat can be held on the working end 1a by surface tension, a reservoirfor holding a quantity of solder is produced by forming a concavity 12in the oblique surface 10. This concavity 12 is, preferablyelliptically-shaped to maximize the surface area to volume ratio. By wayof example only, concavity 12 may have an axial radius of curvatureR_(a) of about 0.269" and a transverse radius of curvature R_(t) ofabout 0.054" with a maximum depth D_(m) of 0.020" when the obliquesurface has a length of about 0.244" in a direction corresponding to themajor axis of the elliptically-shaped concavity 12.

A tip 1, in accordance with the present invention, is especiallyadvantageous for use in soldering leads of an electronic component 15 tolands on the surface of a substrate 20, and avoids the need to eitherfeed solder wire onto a hot soldering iron tip, holding both on a jointto be soldered, or to apply solder onto the soldering tip prior toforming each joint. Instead, after positioning the leads 17 in contactwith said lands 22 and pretreating the leads and lands (as wouldnormally be done), the soldering tip 1 is heated by the soldering device(such as soldering iron 5) and a quantity of solder 24 is melted intoconcavity 12 (FIG. 7), where it is retained by surface tension. Then, bydrawing the solder-containing tip along the region between the leads 17and lands 22 with the quantity of molten solder on the tip 1 makingcontact with this region (as shown in FIG. 8), the molten solder on thesoldering tip will be wicked into the region and solder joints formedbetween the leads and the lands. Further, the inventive tip 1 should beoperated at lower temperatures than the tip of a conventional solderingiron, i.e., at a temperature of approximately 550° to 600° F. As aresult, the operator need not be as skilled to produce proper electricaljoints without solder bridges being formed between adjacent joints; themolten solder at this lower temperature has such viscositycharacteristics as to maximize surface tension between the solder andthe tip.

While I have shown and described only one preferred embodiment inaccordance with the present invention, it is understood that theinvention is not limited thereto, but is susceptible of numerous changesand modifications as known to those skilled in the art. For example,instead of using the soldering iron 5 shown, the tip 1 can be used in awide variety of other types of hand-held soldering devices, such assoldering guns and other solder irons. Likewise, instead of beingchisel-shaped, the working end of the tip may be blade-shaped and thesize, shape and/or proportions of the concavity modified accordingly soas to maximize the quantity of solder which can be retained by surfacetension, without dripping, even when the tip is in it workingorientation (wherein the recess faces downwardly, as reflected by thebroken line representation thereof in FIG. 8). Therefore, do not wish tobe limited to the details shown and described herein, but intend tocover all such changes and modifications as are encompassed by the scopeof the appended claims.

I claim:
 1. A soldering tip for a hand-held soldering device, comprisinga rod of thermally conductive material having an oblique surface formedat one end thereof, and a concavity formed in said oblique surface,wherein said concavity has an elliptical perimetric shape and an arcuatecross-sectional shape, and wherein said concavity forms a reservoirmeans for holding a quantity of solder therein by surface tension.
 2. Asoldering tip for a hand-held soldering iron according to claim 1,wherein the tip is generally chisel-shaped.
 3. A soldering tip for ahand-held soldering iron according to claim 1, wherein the obliquesurface forms a 30° angle with respect to a longitudinal axis of therod.
 4. A soldering tip for a hand-held soldering iron according toclaim 1, wherein the rod is formed of solid copper alloy having an ironplating and a nickel plating over the iron plating.
 5. In a hand-heldsoldering device of the type having a hand-holdable unit with anelectrical heater therein and at least one soldering tip that isdetachably attachable to the hand-holdable unit in heat transferrelationship to said electrical heater, the improvement for maximizingthe quantity of solder holdable on said tip without dripping, comprisingsaid soldering tip being formed of a rod of thermally conductivematerial having an oblique surface formed at one end thereof, and aconcavity formed in said oblique surface, wherein said concavity has anelliptical perimetric shape and an arcuate cross-sectional shape, andwherein said concavity forms a reservoir means for holding a quantity ofsolder therein by surface tension.
 6. A hand-held soldering deviceaccording to claim 5, wherein the tip is generally chisel-shaped.
 7. Ahand-held soldering device according to claim 5, wherein the obliquesurface forms a 30° angle with respect to a longitudinal axis of therod.
 8. A soldering tip for a hand-held soldering iron according toclaim 5, wherein the rod is formed of solid copper alloy having an ironplating and a nickel plating over the iron plating.